Splitting or peeling bark commonly occurs in freezing weather. If it is not weeping or splitting further, then you should just leave it alone to heal on its own. If the area of peeling bark is widening, you can try protective paper (sold at nurseries) to help hold it together while it heals. Do not cover the wound with tar or any other permanent substance as this can trap disease in the wound. In the future, you could try wrapping your trees during winter to provide some insulation.